Self-traveling propping apparatus



G. DOMMANN ETAL l SELF-TRAVELING PROPPING APPARATUS Filed April 13, 1965Oct. 3, 1967 United States Patent G 1o claims. (l. 61-45) ABSTRACT F THEDISCLOSURE This speciiication is directed to a mine roof proppingapparatus which comprises a pair of parallelly-disposed propping memberassemblies which are adapted to operate such that either assembly can bepropelled in a plane substantially parallel to the other assembly whilemaintaining the mine roof in a propped condition. Thus, the two proppingassemblies are adapted to operate in simultaneous or alternate manner.Each of the assemblies comprises a pair of substantially parallelpropping members which are joined together in a generally parallelogramlength, which length is defined by a pair of shackle members/ connectedto the bottom portion of each propping column and a pair of parallel barmembers pivotally connected to the shackle members. By thisconstruction, each propping assembly can be moved as a unit andmaintained during each movement in spaced parallel relationship with theother propping assembly.

This invention relates in general to mine roof propping equipment, andmore particularly to a self-traveling mine roof propping apparatus whichis adapted to move along a mine oor and follow the progress of a'mineralWinning machine.

Self-advancing roof propping systems are being used in increasing extentin the long wall coal mining operations to provide both roof support formine roof areas adjacent to advancing coal winning machines which cutprogressively into the working face of the coal seam. Such prior artpropping systems, like the propping apparatus according to theinvention, are hydraulically or pneumatically driven, preferably viaautomatically controlled hydraulic or pneumatic power systems whichenable the propping system to perform its roof supporting andself-advancing functions in a selected sequence and at a rate suiiicientto accompany the advancement of the coal winning machinery into theworking face.

' The roof propping apparatus of the invention, like the roof proppingsystems of the prior art, have column-like propping members which areextendable and contractable, and can be constructed in the form oftelescopically arranged piston and cylinder hydraulic actuators. Thesepropping members are provided with cap members and shoe members whichare respectively connected to the roof support and floor bearing ends ofthe individual prop columns for respective engagement with the mine roofand oor.

When the propping members are extended, their cap and shoe membersforceably bear against the roof and oor to support the roof and totransmit the roof support icc load from the cap members through the propcolumns and shoe members into the iloor.

In the apparatus according to the invention, four propping members areconnected in pairs by parallelogram linkages to form a pair of roofpropping frames arranged in parallel side by side relation. Thehydraulically operated prop columns of each frame are disposed in spacedapart relation to each other in a plane parallel to their line oftravel. Both prop columns in each frame a-re extended in unison forsupporting the roof, and when the frame is to be immobilized to permitthe other frame to be moved along the mine floor by means of anactuator.

When the prop columns of either frame are extended into roof supportingengagement, the frame is immobilized by reason of the high frictionbetween the shoe members and iloor, which results from the high normalload component of the roof support forces transmitted through the shoes.By retractingrthe prop columns in either frame, this normal load andhence the friction resistance to shoe member sliding can be reduced tozero, or to the extent where that frame can be slidably moved on itsshoe members along the mine oor by means of an actuator which isconnected by cross members to the parallelogram linkages ofthe twoframes.

This advancing actuator, which is preferably constructed with one ormore parallelly connected hydraulic piston and cylinder linearactuators, has its cylinder members connected together by a cross memberto the parallelogram linkage of one frame, and its piston'membersconnected together by another cross member to the parallelogram linkageof the other frame. Y

Thus, when one frame is released, and the other frame is immobilized,the advancing actuator moves the released frame along a line parallel tothe plane of the immobilized frame. When the released frame has lbeendisplaced to a selected position either forward or backward in relationto the immobilized frame, such as a position which corresponds to thelimit extension of the advancing actuator, the released frame can thenbe extended and immobilized, and the formerly immobilized frame can bereleased for movement by the actuator into line with the frame which hasbeen advanced. By repeating this sequence of propping frame shifting,the propping apparatus of the invention can be made to travel under theinfluence of its actuator in a step by step walking manner so as tofollow the progress of a coal winning machine cutting into the workingface.

In a propping apparatus of this type, it is important that theindividual prop columns are maintained in a substantially perpendicularattitude with respect to the mine i-loor. In this way, the proppingcolumns can be utilized to their full load bearing capacity and proppingframe stability is assured. This vertical attitude must also bemaintained when either frame is being advanced.

In addition, it is highly desirable that this perpendicular attitude ismaintained when the prop column shoes pass over irregular contourportions of the iloor.

One of the novel and advantageous features of the propping apparatusaccording to the invention lies in the use of parallelogram linkages formaintaining the prop columns of each propping frame in positionsparallel t0 one another and substantially normal to the floor.

To maintain the propping frames parallel to each other and with theirprop columns normal to the oor, parallelogram linkage type cross membersare used for connecting the frames to their common advancing actuator.

In a preferred embodiment of the apparatus according to the invention,the advancing actuator is constructed as a composite linear actuatorhaving two piston and cylinder hydraulic actuators disposed in parallelrelation to each other, and spaced somewhat closely together forconvenience in an arrangement somewhat resembling that of adouble-barrel shotgun. These individual actuators are preferably of thedouble-acting type to permit the sequential stepwise advancement of thepropping frames.

Both cylinders are ixedly connected together by any suitableconventional fastening means, or if desired, can be bored into a commonblock.

Likewise, the two piston rods which pass through both ends of thecylinders are connected together at their ends, by conventionalfastening means, `such as for example, double shackles. These shacklesare in turn connected to each other by a rigid bar, which can beadvantageously shaped into a cover plate to protect the moving parts ofthe composite advancing actuator. Accordingly, this cover plate extendsparallel to the piston rods protected by it.

The piston cover plate is connected at approximately the center of itslength by a cross member which serves for connecting said piston coverplate to a pair of superposed parallel bars in the parallelogram linkageof one of the frames.

This cross member is preferably constructed in the form of a U-shapedelastic bar harness which is connected at its closed end to the pistoncover plate, and at its two separated ends to the bars of thecorresponding frame parallelogram linkage. The connection of this barharness to the cover plate and parallelogram linkage bars is of a typewhich precludes rotation at the connection points.

A similar bar harness cross member connects the cylinders of thecomposite actuator to corresponding similar superposed bars in theparallelogram linkage of the other frame.

By using elastic bars, such as are commonly used in constructing leafsprings, for the propping frame parallelogram linkages, and asparallelogram linkage cross members connecting the frames to thecomposite actuator, the propping apparatus of the invention is able toperform its propping and self-advancing functions and to maintain anormally directed roof support load transmission into the oor in spiteof local irregularities thereon by reason of the elastic deectionproperties of the bars used in `the frame parallelogram linkages and thecross members.

The U-shaped harnesses can be inserted with their closed ends intopocket-like retainers provided on the cylinders and piston plate cover,and can be secured thereto by means of pin retainers. The free ends ofthese harnesses can be fastened to the parallel elastic coupling bars ofthe parallelogram linkages by clamping them to the bars with a spacerinserted between the coupling bars.

For a more secure frame-to-actuator connection, it is preferable to usetwo U-shaped harnesses disposed parallel to one another and slightlyspaced apart for connecting each frame parallelogram linkage to thecorresponding piston portion or cylinder portion of the compositeactuator.

For the purpose of avoiding unnecessary restriction in the motion of theindividual prop columns of each frame, the two superposed coupling barsof its parallelogram linkage are disposed parallel to each other and inspaced apart relation, and are connected at their extremities by pivotpins to the prop columns of the frame. It is advantageous for the propcolumns to be provided with releasable shackle members for theconnection of the coupling bar ends by the pivot pins. To preventundesired rotation of the prop columns relative to the shackles whichform a part of its parallelogram linkage, said shackles are securedxedly but releasably by means of dowel pins or similar fastening meansto their respective prop columns.

While the coupling bars of the parallelogram linkages could bepin-connected directly to the prop columns of the frames, it isadvantageous to use such intermediate shackle members because in theevent that it becomes necessary to replace individual prop columns ineither of the prop frames, such replacement can be performed expedientlyand economically.

It is therefore, an object of the invention to provide a self-travelingroof propping apparatus for supporting mine seam roofs.

Another object of the invention is to provide a roof propping apparatusas aforesaid which is adaptable for use in mining seams havingirregularly contoured oor's.

Another and further object of the invention is to provide a roofpropping apparatus as aforesaid wherein the support load is borne bystructural members in the apparatus and is transferred to the oor alonglines which are substantially perpendicular to the oor surface.

`Other and further objects and advantages of the invention will becomeapparent from the following detailed description and accompanyingdrawings in which:

FIG. 1 is a schematic plan view of the bottom portion of a proppingapparatus according to a preferred embodiment of the invention, takenfrom a plane passing normally through its propping columns.

FIG. 2 is a schematic side view of a portion of the apparatus shown byFIG. 1.

FIG. 3 is a schematic sectional view taken along the line 3 3 of FIG. 1.

FIG. 4 is a schematic sectional view of the composite advancing actuatorused in the apparatus of FIGS. 1-3, and taken along the line 4--4 ofFIG. 1.

Referring now to FIGS. 1 4 of the drawings, the propping apparatus A ofthe invention comprises a pair of roof propping frams B and C which areconnected to an actuating system D for stepwise relative movement one ata time along spaced-apart parallel travel line paths.

Each of the propping frames B and C is adapted to travel along a minefloor F and has a pair of propping column members 11 which areselectively extendable for supporting engagement with the mine roof (notshown) and are retractable for frame B, C movement along the mine floor.

At the upper, or roof supporting ends (not shown) of columns 11 areconnected cap members (not shown) which Ibear against the roof when saidcolumns 11 are extended, and transmit the roof support load to the floorF through the columns 11 and shoe members 12 which are pivotallyconnnected to the bottom end portions of said column 11.

When the columns 11 on either frame B or C, are extended for supportingthe roof, that frame B, C is substantially immobilized because of thehigh friction resistance to the sliding of the shoe member 12 along theoor F.

On the other hand, when the columns 11 on either frame B or C areretracted out of roof supporting engagement, that frame B or C can beslidably moved along the oor F by the actuating system D.

To provide the aforesaid extension and retraction capability in thecolumns 11, said columns 11 are preferably constructed as telescopicallyarranged hydraulic piston and cylinder actuators which are connected toa suitable conventional hydraulic power source (not shown) through ahydraulic control system (not shown) of conventional construction.

The propping column members 11 are disposed in spaced-apart parallelrelation to each other in a plane parallel to the line of travel oftheir corresponding frame B, C.

Parallelogram linkages G are provided for maintaining the columns 11 ineach of the frames B, C in a mutually parallel spaced relation, with thecolumns 11 i'n each frame being connected together by a parallelogramlinkage G.

As can be seen in greater detail in FIG. 2, each parallelogram linkage Gcomprises a pair of shackle members 13 mounted to the lower portions ofthe columns 11, and a pair of parallel spaced-apart bars 15 which arepivotally connected at their ends to the shackles 13 by means of pins16.

The columns 11 in each of the frames B, C are maintained in parallelrelation to each other by the action of the parallelogram linkages G,which because the pivot connection axes established by the pins 16 areperpendicular to the plane of said columns 11, permit only equallyan-gular shifting of the columns 11 in said plane. Because of the fixedconnection of the shackles 13 to the columns 11, and the arrangementofthe relatively at bars 15 with their most -rigid section perpendicularto the plane of the columns 11, substantially no relative twistingmovement of the columns 11 in either frame B, C can occur.

The shoes 12 are articulately connected to the bottom end portions ofthe columns 11 by means of pivot pins P, and are of such length andbreadth as to be capable of spanning irregular portions of the floor F.As will be apparent to those skilled in the art, by providing pivotallyconnected shoes 12 of appropriate lateral dimensions on each column 11,the propping apparatus A can be adapted to travel along mine floors Fhaving any normal range of irregularity in elevation contour, and at anylocation on said iloor F, the propping frames B and C of said apparatusA can be extended for supporting the roof with the columns 11 beingmaintained substantial-1y perpendicular to the average local floorcontour.

The actuating system D includes a pair of co-extensive superposedhydraulic actuators H disposed in parallel relation to each other andhaving cylinders 17 and pistons 18 which are respectively connectedtogether for operation in unison.

The connection of the cylinders 17 is preferably achieved by boring intoa common casting block, but any other suitable fastening means (notshown) can be substituted for iixedly connecting said cylinders 17together.

The piston rods 18 which extend beyond the ends of the cylinders 17 andare xedly connected together at their ends by means of double shackle19. These shackles 19 are in lturn xedly connected to a cover bar 20vwhich also serves for protecting the working parts of the actuators Hfrom damage, and the operating personnel from injury by contact withsaid actuators H.

The cover bar 20 extends in parallel spaced-apart relation to the pistonrods 18 and cylinders 17, and along the length thereof.

To utilize the relative motion of the pistons 18 and cylinders 17 in theactuating system D for moving the frames B and C relative to each other,parallelogram type cross members K are used for operatively connectingthe cylinders 17 to the parallelogram linkage G of one of the frames B,C, and for operatively connecting the pistons 18 via their attachedcover bar 20 to the parallelogram linkage G of thelother of said framesB, C.

The cross members K also serve to maintain the frames B and C inlaterally spaced-apart relation to each other, so that they travel alongparallel paths of constant spacing when driven by the actuating systemD.

For this purpose, the cross member K arrangement is preferablyconstructed with pairs of oppositely disposed U-shaped harness members21, which can be constructed of at bar stock bent into a U-shape, wtihone of said harness members 21 in each pair being connected at itsclosed end portion to the pi-ston cover bar 20, and the other harnessmember 21 in each of said pairs being connected at its closed endportion to the integral cylinder block 30. The free ends of the harnessmembers 21 are connected to the bars 15 of the parallelogram linkages Gon corresponding propping frames B and C.

To accommodate the securing of the closed end portions of the harnessmembers 21, the cover bar 20 and cylinder block 30 are preferablyprovided with shackle members 24 which are ixedly attached as by weldingthereto. Each of the shackles 24 is provided with a pair of retainerpins 23 for securing the closed end portions of the harness member 21passed through the slotted pocket openings between the pins 23, shackles24 and the cover bar 20 or cylinder block 30 to which said shackles 24are mounted. The pins 23 are inserted into the shackle 24 lugs whichextend from the cover bar 20 and cylinder block 30 and are orientedsubstantially parallel to the direction of piston 18 and cylinder 17motion. In this manner, a harness member 21 to actuating system Dfastening is achieved in both a simple and expedient manner thatsubstantially precludes relative rotation between the harness members 21and actuator system D about any axis other than those of the pins 23.

The free end portions 25 of the harness members 21 are connected to thetwo s-uperposed coupling bars 15 on each propping frame B and C by meansof clamping bolts 26 which clamp said end portions 25 between spacers 27and the inwardly facing surfaces of the bars 15.

In-the propping apparatus A thus far described, the propping frames Band C are similarly constructed for interchangeability, and to permitsaid frames B and C, and the actuating system D to be transported asseparate units which can be assembled at the work site in the mine.

As shown by way of example in FIGS. l and 2, four harness members 21(two pairs) are used in the cross member K to provide a more stablestructural connection between the actuating system D and the frames Band C. If desired, additional pairs of similarly connected harnessmembers 21 can be provided, or a single pair of harness members 21 ofgreater Width, but bent into the same type of U-shape can be substitutedfor the two pairs of narrower harness members 21 shown.

At the work site, the four U-shaped harnesses 21 are assembled to theactuating system D by inserting the pins 23. Then the propping frames Band C are coupled to the actuating system D by means of the cross memberK by inserting and tightening the clamping bolts 26.

Since the actuating system D is constructed as a double cylinderactuator, and is fastened via coupling bars '15 to the propping frames Band C and by the two spacedapart pairs of U-shaped harnesses 21, saidcoupling bars 15 and harness members 21 being relatively elastic, in amanner similar to steel `leaf springs with regard to loading indirections parallel to the columns 11 (i.e. perpendicular to the floorF), and relatively stiff as regards loading in planes perpendicular tothe columns 11 and parallel to the floor F, the apparatus A is providedwith the necessary structural rigidity to maintain its propping frames Band C in their intended spaced-apart parallel positions for stepwisetravel along parallel line paths and yet have sufficient yieldingcapability for adaptation to the mine floor F contour irregularities.This elastic yielding is assured not only by the elastic material andarrangement of the harnesses 21 and coupling bars 15, but also by thepins 16 which connect said coupling bars 15 with the columns 11, saidpins 16 being in spaced-apart relation to each other and arranged inmutually parallel relation.

In the operation of the apparatus A, only one of the proppin-g frames Bor C is moved at a time. For example, if it is desired to move the frameB, the frame C is extended for roof supporting engagement and therebyimmobilized, with the frame B being retracted so as to be slidable alongthe oor F. This is necessary because one movable member, either thecylinder block 30 or the piston bar 20 of the actuating system D must beconnected to the fixed frame C, and the other movable member must beconnected to the frame B that is to be moved. For example, the cylinderblock 30 is connected for movement with the frame B, with the piston bar20 being connected for movement with the frame C.

The actuating system D is then energized to move the frame B along itsline of travel for a selected distance relative to either end of thefixed frame C, up to the extension capability of the actuators H. Withframe B thus advanced, it can be extended and thereby immobilized toserve as the fixed frame for advancing the frame C, which is thenreleased from its previous roof supporting engagement.

To advance frame C relative to and in line with the frame B, theactuating system D is again energized, but in this case the cylinderblock 30 is held fixed along with the frame -B and the piston bar 20 ismoved with the frame C.

Thus, by repeating the aforementioned sequence of operations, thepropping apparatus A can be moved either backwards or forwards along themine oor F by sequential stepwise movement of its frames B and C in amanner similar to walking, except that the frames B and C are not liftedup from the oor F when moved, but rather slide along said oor F upontheir shoes 12.

As will be apparent to those skilled in the art, the control of thepropping apparatus A movement can be simply accomplished by means of aconventional hydraulic control system (not shown) which is connected toa hydraulic power source (not shown) and to the actuating system D forcontrollably energizing same to perform the desired frame B, C shiftingmovements.

The same hydraulic power source used for extending and retracting thepropping columns 11 can be used for operating the actuating system D, ifdesired. Likewise, the hydraulic controls for the actuating system D canbe integrated with those used for controlling the columns 11.

It is advantageous to provide such an integrated control system withinterlocked control means to prevent attempted movement of an extendedand thus locked frame B, C, since normally, both frames B and C will beextended for supporting the roof prior to any movement of the apparatusA.

As can be appreciated by the artisan, there are numerous apparentvariations and modifications which can be implemented into the apparatusA according to the invention to adapt said apparatus A for expedientoperation in a particular application.

What is claimed is:

1. A self-traveling mine roof-propping apparatus which comprises:

(a) a first roof-propping frame which is adapted to travel along a minefloor and is extendable for supporting engagement with the roof, saidframe being substantially immobile when extended .for roofsupportingengagement, said frame having a pair of propping column members disposedin spaced-apart parallel relation to each other in a plane parallel totheir line of travel;

(b) a first parallelogram linkage; comprising a pair of shackle members,each of which being xedly connected to the fbottom portion of a proppingcolumn in the frame, and a pair of superposed parallel bar members ofsubstantially equal length disposed in spaced-apart relation andpivotally connected at their ends to said shackle members, whereby saidparallelogram is defined by a pair of oppositely disposed parallel barmembers and a pair of oppositely disposed parallel shackle prop columnmembers; connecting the propping columns of said first Iframe to eachother in mutually spaced parallel relationship;

(C) a Second roof-propping frame, similar to the rst, disposed inlaterally spaced-apart parallel relation thereto for travel along a lineparallel to the line of travel of said first frame;

(d) a second parallelogram linkage; comprising a pair of shacklemembers, each of which being iixedly connected to the bottom portion ofa propping column in the frame, and a pair of superposed parallel barmembers of substantially equal length disposed in spacedapart relationand pivotally connected at their ends to said shackle members wherebysaid parallelogram is defined by a pair of oppositely disposed parallelbar members and -a pair of oppositely disposed parallel shackle propcolumn members; connecting the propping columns of said second `frame toeach other in mutually-spaced parallel relationship;

(e) linear actuating means for sequentially moving said first and secondpropping frames relative to each other and in side by side relationalong parallel line paths; and

(f) cross member means connecting said actuating means to said first andsecond parallelogram linkage means whereby said rst and second framemembers can be moved one at a time along their respective paralleltravel lines, with one of said frames being extended in roof-supportingengagement and thereby immobilized while the other frame is movedrelative thereto by said actuating means.

2. The apparatus according to claim 1 including means for rigidlyfastening the cross member means to the actuating means and to eachparallelogram linkage means to prevent rotation of the propping framesrelative to each other.

3. The apparatus according to claim 1 including an individual shoemember articulately connected to the bottom portion of each proppingcolumn to facilitate the movement of the propping frames upon said shoemembers along the floor.

4. The apparatus according to claim 1 wherein the parallel bar membersare pivotally connected to the shackle members with pivot connectionaxes that are perpendicular to the plane of the propping columns incorresponding propping frames.

5. The apparatus according to claim 1 wherein the linear actuating meansincludes a pair of coextensive superposed piston and cylinder hydraulicactuators disposed in parallel relation to each other, fastening meansconnecting the pistons of said actuators together, and fastening meansconnecting the cylinders of said actuators together for operation inunison.

6. The apparatus according to claim S wherein the piston and cylinderhydraulic actuators are both double acting linear actuators havingpiston rods projecting beyond both ends of their correspondingcylinders, with the ends of said piston rods being tixedly connected t0a cover =bar by shackle connector means, said cover bar extending inparallel spaced-apart relation to said piston rods, and being connectedto the cross member means for transmission of piston rod motion to apropping frame.

7. The apparatus according to claim 6 wherein the cross member meansincludes at least one pair of oppositely disposed U-shaped harnessmembers, one of said harness members in each pair being connected at itsclosed end portion to the actuator piston cover bar, and the other ofsaid harness members in each pair being connected to the actuatorcylinders, with the open end portions of said harness members beingconnected to the parallelogram linkages on corresponding proppingframes.

8. The apparatus according to claim 7 wherein the open end portions ofthe harness members are secured by clamping to the parallel barredmembers of the parallelogram linkages, and including spacer meansdisposed between said parallel bar members at the clamping points of theharness members for maintaining a selected bar spacing thereat.

9. The apparatus according to claim 7 wherein the closed end portions ofthe harness members are secured to the cylinders and the piston coverbar by means of shackle members fastened thereto and pin membersextending through said shackle members, with the closed end portions ofsaid harness members being passed between corresponding pin members Iandshackle members.

10. The apparatus according to claim 7 wherein two pairs of oppositelydisposed harness members are provided for connecting the piston coverbar and cylinders to corresponding parallelogram linkages, said pairs ofharness members being connected to said cover bar, cylinders andparallelogram linkages in parallel spaced-apart relation to each other.

1 il References Cited UNITED STATES PATENTS 10/1963 Barall et al. 6145.27/19'65 Herrmann et al 61-452 ERNEST R. PURSER, Primary Examiner.

1. A SELF-TRAVELING MINE ROOF-PROPPING APPARATUS WHICH COMPRISES: (A) AFIRST ROOF-PROPPING FRAME WHICH IS ADAPTED TO TRAVEL ALONG A MINE FLOORAND IS EXTENDABLE FOR SUPPORTING ENGAGEMENT WITH THE ROOF, SAID FRAMEBEING SUBSTANTIALLY IMMOBILE WHEN EXTENDED FOR ROOFSUPPORTINGENGAGEMENT, SAID FRAME HAVING A PAIR OF PROPPING COLUMN MEMBERS DISPOSEDIN SPACED-APART PARALLEL RELATION TO EACH OTHER IN A PLACE PARALLEL TOTHEIR LINE OF TRAVEL; (B) A FIRST PARALLELOGRAM LINKAGE; COMPRISING APAIR OF SHACKLE MEMBERS, EACH OF WHICH BEING FIXEDLY CONNECTED TO THEBOTTOM PORTION OF A PROPPING COLUMN IN THE FRAME, AND A PAIR OFSUPERPOSED PARALLEL BAR MEMBERS OF SUBSTANTIALLY EQUAL LENGTH DISPOSEDIN SPACED-APART RELATION AND PIVOTALLY CONNECTED AT THEIR ENDS TO SAIDSHACKLE MEMBERS, WHEREBY SAID PARALLELOGRAM IS DEFINED BY A PAIR OFOPPOSITELY DISPOSED PARALLEL BAR MEMBERS AND A PAIR OF OPPOSITELYDISPOSED PARALLEL SHACKLE PROP COLUMN MEMBERS; CONNECTING THE PROPPINGCOLUMNS OF SAID FIRST FRAME TO EACH OTHER IN MUTUALLY SPACED PARALLELRELATIONSHIP; (C) A SECOND ROOF-PROPPING FRAME, SIMILAR TO THE FIRST,DISPOSED IN LATERALLY SPACED-APART PARALLEL RELATION THERETO FOR TRAVELALONG A LINE PARALLEL TO THE LINE OF TRAVEL OF SAID FIRST FRAME; (D) ASECOND PARALLELOGRAM LINKAGE; COMPRISING A PAIR OF SHACKLE MEMBERS, EACHOF WHICH BEING FIXEDLY CONNECTED TO THE BOTTOM PORTION OF A PROPPINGCOLUMN IN THE FRAME, AND A PAIR OF SUPERPOSED PARALLEL BAR MEMBERS OFSUBSTANTIALLY EQUAL LENGTH DISPOSED IN SPACEDAPART RELATION ANDPIVOTALLY CONNECTED AT THEIR ENDS TO SAID SHACKLE MEMBERS WHEREBY SAIDPARALLELOGRAM IS DEFINED BY A PAIR OF OPPOSITELY DISPOSED PARALLEL BARMEMBERS AND A PAIR OF OPPOSITELY DISPOSED PARALLEL SHACKLE PROP COLUMNMEMBERS; CONNECTING THE PROPPING COLUMNS OF SAID SECOND FRAME TO EACHOTHER IN MUTUALLY-SPACED PARALLEL RELATIONSHIP; (E) LINEAR ACTUATINGMEANS FOR SEQUENTIALLY MOVING SAID FIRST AND SECOND PROPPING FRAMESRELATIVE TO EACH OTHER AND IN SIDE BY SIDE RELATION ALONG PARALLEL LINEPATHS; AND (F) CROSS MEMBER MEANS CONNECTING SAID ACTUATING MEANS TOSAID FIRST AND SECOND PARALLELOGRAM LINKAGE MEANS WHEREBY SAID FIRST ANDSECOND FRAME MEMBERS CAN BE MOVED ONE AT A TIME ALONG THEIR RESPECTIVEPARALLEL TRAVEL LINES, WITH ONE OF SAID FRAMES BEING EXTENDED INROOF-SUPPORTING ENGAGEMENT AND THEREBY IMMOBILIZED WHILE THE OTHER FRAMEIS MOVED RELATIVE THERETO BY SAID ACTUATING MEANS.